Tenjou Tenge's OP was literally what sparked my renewed interest in anime last year. I'd seen the opening as a trailer years ago but never went and watched the show until a few months ago when I heard the song again.

It was only bad because of the pacing, it could be so much better if they remade it and didn't devote a third of the show to flashbacks. I think there's too much potential for epic fight scenes to let it go to waste.

I don't watch that much anime but I guess from recent memories I would say Kingdom's OP.
Pride by Nothing's Carved in Stone.
The video is pretty standard in any season version but the song is SO addicting!

Only one comes in mind: GUNDOH MUSASHI OP! That OP is very catchy, and the starting part is one heck of an eargasm. Not to mention that the opening sequence is one of the most innovative I've ever seen.